Cabin pressure change control



1396- 1952 J. B. COOPER ETAL CABIN PRESSURE CHANGE CONTROL OriginalFiled Oct. 18, 1941 3 Sheets-Sheet 2 I Zinnentbf James BL C 09 Alfred BJepgon attorney:

Dec. 16, 1952 J. B. COOPER ETAL CABIN PRESSURE CHANGE CONTROL OriginalFiled OGc. 18, 1941 3 Sheets-Sheet 5 3nnentorg Alfred B. Jcpson James 5;Cooper Clttomegg Patented Dec. 16, 1952 UNITED STATES PATENTiOIFiFiIiCiE CABEN PRESSURE CHANGE CONTROL James E. Cooper, Seattle, andAlfred-B, Jepson, Bellevue, Wash, assignors to Boeing Airplane Company,Seattle, Wash, a corporation of Delaware Original application Octoberl8,1941, Serial-No.

Divided and this application October 9, 1948, Serial N0. 53,686

25 Claims. 1

Relation to other devices The patent to N. C. Price, Reissue 22,272,issued February 16, 1943, discloses a pressure control system and apressure control device intended to regulate the pressure within anaircraft cabin. In the physical form adopted iorillustration in thatPrice patent, an inflow valve and an outflow valve were employed, withinterconnecting controls afiecting each of the valves, theseconapplication Serial No. 415,602, new patent No.

2,450,881, filed October 18, 1541 for Pressure Cabin Controls. Itisintended for use in conjunction with other devices which operate tosupply air under pressure within the cabin. These other devices may beso operated as to regulate the amount or vary the pressure of the-airwhich is supplied to the cabin, in accordance with altitude or pressureconditions. The present device may operate (see Figure 3) whollyindependently or" the pressure-supplying means, or (see Figure l) it maybe connected to the latter to induce compensating adjustment in thelatter. The system as a whole, and especially these other devices, aremore fully disclosed, and are claimed, in our copending applicationSerial No. 415,603, filed October 18, 1941.

'The present device, in the embodiment illustrated and chosen by way ofexample, is in the nature of an outflow valve with two regulating orcontrolling means, one of which is an absolutepressure sensitive device,and the other of which is a differential-pressure sensitive device,these two devices operating in a manner and to an end similar to theoperation of similar devices in the Price patent, but operating now upona, single valve means to control outflow, rather than acting jointly andcooperatively upon aninflow and an outflow valve means, as in the Pricepatent. When we speak of a single valve means, it is-to be understoodthat normally duplicate valve means would be employed, each of whichalone would suflice, and each. of which is such a single valve .means.

2 Reference is also made to the copending Price application, Serial No.216,028, filed June 27, 1938, which discloseshow itis possible toregulate and -to vary therate of pressure change in thecabinindependently of the rate of ascent or descent, more especially, inaccordance with a time factor. By the invention therein disclosed it ispossible to effect a given change of cabin pressure in a givenperiod oftime, whether ornotithere is any change of altitude of theairplane, andif there is a change of altitude, regardless of the rate of that change.The same sort of regulation can be effected in the present invention.

If duplicate valve means are employed, one

onlymay be provided with certain adjustments, ,forinstancetheadjustments 'for regulating the rate of pressure change inaccordance with a time factor, and theother may not haveany similarregulation. Preferably all will have an overriding dilTerential-pressuresensitive device limiting the attainable difference of cabin pressureover external pressure, and, coupled therewith, suchother-controls oradjustments as are desired, but not necessarilyevery valve provided withall such other controls or-adjustments. In all cases such valves orduplicate valves willcontrol and permit continual outflow, except as onemaybe ,a standby valve operative only when another General purposes Bythe arrangement of this invention it is possible to effect unified andsensitive control of the outflow valve means, thereby tending tomaintaincabin pressures automatically more nearly at the intended-pressures.Thus without manual operation the cabin pressure may be-caused to followa selected line or graph (see Figure 2), and

these values, by certain manually or mechanically changeable means,under control, can be varied to suit different conditions, but alwaysfor any given setting the values of pressure within the cabin will bemaintained automatically closely approximat-ing the intendedvalues-assuming always sufiicient capacity in and proper functioningofthe pressure supply-devices and controls.

Generally speaking, thenaccording to the present invention there isprovided'a device for controlling or regulating automatically thepressure within a cabin, which pressure is built up by other means,which will permit a certain amount of outflow and therefore provide forproper ventilation of the cabin, which will tend to compensate for, butnot to govern, changes in the ventilating rate, independently inducedand regulated, and which will operate automatically in accordance withtwo control devices, one of which may be an absolute-pressure sensitivedevice and the other of which may be a differential-pressure sensitivedevice, to the end that the cabin pressure may be maintainedautomatically at desired values for any given altitude; and which,upwards above the point at which the cabin pressure reaches a selectedlimiting differential pressure, will not permit the cabin pressure toexceed that differential pressure, whether the tendency to exceed thesame arise from an increased rate of supply of air under pressure withinthe cabin, or from a decrease in the external pressure with increase ofaltitude.

By way of example, the cabin pressure may be maintained, from sea levelup to a selected critical altitude, substantially equal to the externalpressure; from that altitude up to a selected higher altitude the cabinpressure may be maintained at a value or values higher than the externalpressure, but not exceeding a selected differential, and may indeedfollow almost any given curve or graph from almost any point ofdeparture from the atmospheric pressure line to the limitingdifferential pressure line.

It is also an object to provide a control functioning in accordance witha time factor, as, a rate-of-pressure-change control, or a controloperating for a given period of time, which will regulate the cabinpressure conjointly with, as modified by, or independently of, the othercontrols mentioned above.

With these objects in mind and others, particularly those which pertainto the mechanical construction and arrangement of the device, as willappear from the following specification, our invention comprises thenovel parts, and the novel combination and arrangement of the same, bothper se and with relation to the pressure cabin and to the air supplymeans, as is shown in the accompanying drawings, described in thisspecification, and as will appear more fully from the appended claims.

The drawings The accompanying drawings illustrate the invention in aform which has been found practical, though it will be understood thatvarious changes in the form, character, and arrangement of the parts maybe made in accordance with the principles to be made clear hereafter.

Figure l is in general an axial section through the outflow valve andthe control mechanism, illustrating the parts in the low altitudeposition, that is, the position wherein the cabin pressure issubstantially the same at all altitudes as the external pressure.

Figure 2 is a graph illustrating the pressure curve which the cabinpressure will follow automatically upon the normal or usually intendedoperation of the device of our invention.

Figure 3 is a diagrammatic showing of a pressure cabin, showing thedevice of the present invention incorporated therein as a pressurecontrol device entirely independent of the pressure supply source,likewise associated with'the pressure cabin, and Figure 4 is a similarview show- ,ing the device of the present invention arranged to producecompensating action in the pressure supplying means.

Figure 5 is a wiring diagram, illustrating how the normal operation ofthe device of this invention may be altered to produce difierenteffects, and in particular to produce a change of pressure in the cabinat a rate which is different from the rate which would be imposed by theactual rate of ascent or descent of the airplane.

Definitions This application deals with pressures and pressure relationsthat are seldom stable. An absolute pressure that might under givenconditions be regarded as positive, or high, will under other conditionsbe regarded as negative, or low. These terms, or the terms plus pressureand minus pressure, are to be understood always as related to theimmediately obtaining conditions, rather than as absolute terms.

The valve will be described as operable by a servomotor, which, asherein shown, takes the form of an air motor, operated by a differenceof pressure. The terms servo means or servomotor are to be understood asincluding any suitable device, and not necessarily that described ifanother is suitable.

In the air motor a diaphragm is disclosed, but the term diaphragm is tobe understood as including a piston, which is a special form ofdiaphragm, or any suitable pressure-actuated device. Likewise, the termpistonparticularly as used in describing the differential-pressuresensitive device-is intended to include any form of diaphragm.

Considerations governing design A pressure cabin airplane designed forpossible use under a variety of conditions must necessarily operate as acompromise between conditions which might obtain at one time, andconditions that might obtain at a diiferent time, or under differentcircumstances. Obviously the conditions which obtain upon take-off fromor landing upon a landing field which is at an elevation of severalthousand feet are different from those which obtain upon take-off fromor landing upon a landing field which is close to sea level. The designof the pressure cabin control must take into account the possibility oftake-oil or landing now at the more elevated field, and again at thelower field, and generally it has been considered that the fundamentalconsiderations which must be brought to a satisfactory compromise in theselection of the pressure altitude relationship to be obtained in such acontrol are the following:

1. An optimum absolute cabin pressure which is sufficiently high toavoid impairing the safety and comfort of operating personnel andpassengers, and sumciently low to avoid the probability of landing on alanding field at a high elevation with the cabin in an inadvertentlysupercharged" condition;

2. A maximum differential between cabin and atmospheric pressures whichwill not impose prohibitive structural requirements on the cabin; and

3. A maximum ratio of cabin absolute pressure to atmospheric pressurewhich will not necessitate inordinate weight, size, or power consumptionof the compressor.

Performance characteristics In view of these considerations it iscurrently accepted that operations in the range from sea level-a inFigure 2 up to an appropriately chosen critical altitude, representedatb or I),

should be unsupercharged, that is, the cabin pressure should besubstantially thesame as the external pressure, represented by the linea'-b'-c'-d that the cabin pressurewhich obtains at this criticalaltitude, for instance, 8,000

feet, should be maintained during ascent, as by the line b-c, until thedifferential pressure reaches a maximum safe and economical value,

equivalent to 11,000 feet, for example, reached ati30,000 feet altitudebetween c-and c' in Figure 2; and that this limiting differentialpressure .c'c should be, or can well be maintained, along thecurve c-d,so long as the aircraft continues above the altitude at which thisdifferential pressure was reached, and so long as the pressuresupplydevices can continue to supply adequate air under pressure within thecabin. In the .graph, Figure 2, the difference a'a represents the pluspressure due to continuous inflow and restricted outflow.

It must be borne in mind, of course, that the pressures may vary fromthe accepted graph abcd thus outlined; for instance, it may bepreferred, instead of commencing to supercharge only when the criticallow altitude has been reached at b, to start supercharging at take-01for at some altitude g lower than that at which normally it wouldcommence automatically, and

'the'cabin pressure may be altered at will and at such rate as may bedesired, the lower limits of pressure being always the atmospheric curvea'bc' d', and the'upper limits being always the differential pressurecurve nk-cd, or that curve extended to higher altitudes.

It is possible, too, to anticipate a pressure change,-and without actualchange of altitude to accomplish a change of cabin pressure, as from 9'to k, and then to m. Always, and regardless of the part of the field ofaction chosen, the diiferential-pressure sensitive device is a sentinelto prevent that difierential being exceeded, to the possible detrimentof the cabin structure.

Reference is made to the patent of James E. Cooper, one of theco-inventors herein, No. 2,307,199, issued January 5, 1943, toillustrate the possibilities of controlling the rate of pressure change,and of operating other than along an unvarying graph.

For a further understanding of the manner of operation of the device andthe principles governing the same, reference is made to the copendingPrice application, Serial No. 216,028, re-

ferred to above, and particularly to Figure 3 therein.

Figure 2, representing at abcd an ex- .ample of the normal manner ofoperation of the present device in an actual airplane, shows that .therewill be no essential supercharging eifect so :higherthan most landingfields. The 8,000 foot pressure altitude will then be maintained withinthe cabin until the limiting differential pressure of 13.34 inches ofmercury is reached, which will normally occur at an altitude of 30,000feet. At altitudes above 30,000 feet the limiting differential pressureof 13.34 inches of mercury will be maintained until the compressor orequivalent means to supply air under pressure within the cabin becomesincapable of producing the required pressure rise.

The cabin and air supply evices :In the drawings the skin of theairplane is :represented at 9, and this skin is so constructed ,as tobereasonablyair-tight for all internal pressures which do not exceed theexternal pressure by more ,than the selected differential. This ispurely adesign matter, and the skin can be-made suiiiciently tight .tohold any desired differential, but it is scarely economical andpractical to attempt to hold sea level pressure up to the ceiling of theaircraft since this would require such structural complications andadded .weightas to make the airplane economically impractical. The skin9 is tight against. reasonable leakagaalthough some leakage is bound tooccur, particularly as the differential limit is aproached or reached.

As is seen in Figures 3 and 4,.air is supplied under pressure within theskin 9 by means which are represented as the blower vBildriven from asuitable source of power, such as a propelling engine 9!, through aspeed varying device indicated at 92 and controllable bythe deviceindicated collectively by the numeral 93. Control is effected inaccordance with pressure conditions and flow conditions, or iscontrolled in any suitable manner, the control being represented as thepressure sensitive device 93a connected at 94 and 93 respectively to aduct leading to or from the blower and to a Venturi diffuser 96 or 96awithin that duct. The pressure-sensitive device 93 may also be sensitivethrough a duct 93b (see Figure 4) to the cabin pressure. Withoutdescribing the arrangement in further detail, itmay .besaid that theblower will supplyair under pressure within the cabin 9 through the duct9012 at a rate which is sufficient, Within the capacityof the blower, tomaintain a cabin presbe said at this point concerning the same.Reference is made to that copending application for a fullerunderstanding of the air supplying means, and to a later point in thisspecification for an explanation of its operative relationship to thepresent control device.

The pressure control device The construction and operation of thepressure control may be best understood by following through a cycle ofoperation. Figure 1 shows the position of parts at low altitudes, wherethe cabin is substantially unsupercharged, but where the airis beingsupplied-by the air supply means :in a manner-and at a rate which,without proper 7 operation of the pressure control device, would efiectsupercharged operation.

Condition A In this range of altitude cabin pressure in excess ofatmospheric pressure is not required, although a small pressuredifierential will usually exist because of the restricted escape of thenormal quantity of ventilating air which enters the sealed cabin '9through the compressor or through independent fresh air scoops.

The valve I controlling outflow from the cabin 9 tends to seat upon adifiuser seat 2 by virtue of the low pressures which are existent on thelower surface of the valve as shown and which are partially due to theVenturi action of the air passage, and partially due to any differentialpressure existing between the cabin and the atmosphere. This action isindependent of the attitude or positioning of the valve. If the valve ismounted in the vertical position, as shown in the preferred arrangementof the drawings, gravity forces will tend to seat it, in addition to thefluid pressure-created forces. The valve I is carried upon a spindle I0,guided for axial movement at II, and upon the upper end of this spindle,above the partition 28, is secured a sealing diaphragm l3 backed by thepiston I2. The pressures due to the outflow of air, and for somepositions of installation, the weight of the diaphragm and valveassembly, would normally seat the valve at 2 to close ofi outflow fromthe cabin.

It is evident that a suitable differential pressure acting upward acrossthe diaphragm I3 will overcome the gravitational force and any otherforces which act downward upon valve 1, and will thereby cause thediaphragm and valve assembly to rise, particularly since the efiectivearea of the diaphragm I3 is somewhat greater than that of valve I.

To assist in holding the assembly raised, once the valve is open, thespace I! above the hollow valve body I is in communication with a lowpressure source. As shown, it is provided with vent holes I4, locatedsomewhat below the portion of the valve which seats upon the diffuser,but being approximately in the throat of an annular venturi formedbetween the open valve and the diiiuser seat, and the interior of thespace H thus formed between the hollow valve I and the partition 20 isopen to cabin pressure past a needle valve I5, which restricts access ofcabin'pressure to the chamber IT. The pressure within the chamber I1 isreduced by suction through the vent holes I4, tending to resist closureof the valve i. Leakage past the lip of the valve I where it slideswithin the cylinder 2| may somewhat alter these conditions, but issmall, and can be compensated for by adjustment of the needle valve I5,or if preferred, leakage at this clearance can be eliminated by theemployment of a sealing diaphragm between the casing part 21 and the lipof the valve, similar to the diaphragm I3.

In lieu of the holes I I in the valve I an alternate arrangment is toconnect chamber I! to the passage between valve I and diffuser seat 2 orany source of lower pressure by means of an exterior tube. If theeffective area of the diaphragm I3 is sufliciently large, the provisionsdescribed above will be unnecessary for the operation of the control.

The chamber 22 beneath the diaphragm I3 is in free and opencommunication with the interior of the cabin, and of course to the cabinpressure, through a vent 23. Cabin pressure therefore acts upwardly uponthe diaphragm I3 and the diaphragm and valve assembly, tending to holdthe valve upraised in opposition to gravity and other forces, and thefinal control for the diaphragm and valve assembly therefore dependsupon the negative pressure withinthe chamber 24 above the diaphragm. Airfrom the cabin, under pressure, enters the chamber above the diaphragmI3, past the needle valve I6, and escapes through the port 25 andextension tube 28 under certain conditions-these conditions including aneiiective connection from the tube 26, as by way of the tube 21, to asource of minus or low pressure. throat of the annular venturi adjacentthe difiuser seat 2. Another source might be external atmosphere,particularly at appreciable altitudes, or the vacuum system of theairplane.

For the condition of operation now under consideration air flows awayfrom the chamber 24 "without appreciable restriction, and if the needlevalve I6 is properly adjusted it will restrict the flow of air from thecabin sufficiently to cause a reduction in pressure relative to thecabin pressure above the diaphragm I3. This is additive to any reductionof pressure within the chamber IT. Under such circumstances even aSlightly lower external pressure communicated through the tube 2'? tothe chamber 24, or even a slightly higher cabin pressure acting throughthe port 23, will cause the valve I to open, and thereby prevent anincrease in cabin pressure relative to external pressure.

It is desirable, but not entirely practical, that this condition ofoperation should persist throughout the range of altitudes at which theaircraft will normally be operated. It is not entirely practicable forthe reason that it will occasionally be necessary for the airplane toclimb to such altitude that altitude effects may be felt by the crew orthe passengers, and before this can occur supercharging should becommenced. At a suitable cabin pressure altitude this form of operationterminates, and supercharging begins.

Upon the attainment of a selected critical low altitude, yet where theatmospheric pressure is suificiently low that it is desirable forsupercharging to commence, the cabin pressure, acting upon the evacuatedSylphon bellows 3, which may be considered an absolute-pressuresensitive device, becomes inadequate to equilibrate the combinedexpansive forces exerted by the spring 30 and by the resiliency of thebellows itself. Consequently the bellows begins to expand. Upon itsexpansion, assisted by the spring 39, in an upward direction in thedrawings, its head 3| acts upon the metering in 33 to restrict the flowof air through the orifice 34 in the slidable plug 32, which isinterposed between the tube 26 and the outlet tube 27. This restrictsthe flow of air from the upper side of the diaphragm i3 through theorifice 34, and thus tends to equalize the pressure across the diaphragmI3, causing the valve I to move towards its seat, as previouslyexplained. Closing movement of the valve, unless accompanied byprecisely corresponding reduction of pressure of the iniiowing air tothe cabin, which does not ordinarily occur, increases the cabinpressure. This in turn causes recompression of the bellows 3 andreopening of the orifice 34 to the passage of air from the upper'side ofthe diaphragm I3, which results in the reopening of the valve I and aconsequent reduction of cabin pressure.

It is clear that the foregoing action would result in a repetitiouscycle of instability wherein A convenient low pressure source is the thevalve would hunt and the cabin absolute pressure would oscillate betweenvalues slightly above and slightly below the preselected critical valueat which the bellows 3 begins to expand. This undesirable effect isovercome by the linkage of the valve l to the orifice at through theplunger- 40 and rocker arm 35, the fulcrum of which is at 36, and whichmay have its longer arm pulled downwardly by the spring 31. As the valveI closes in response to expansion of the bellows 3 the orifice 34 iswithdrawn slightly from the metering pin 33, thus tending to reopen thepassage through the orifice 3t and to check the downward travel of thevalve I. Conversely, as the valve opens to relieve superfluous air fromthe cabin the orifice 34 descends upon the metering pin 33, and'therebyrestricts the flow of air from the upper side of the diaphragm I3; andchecks the upward travel of the valve I. It can thus be seen that as thevalve begins to move in either direction in response to change in cabinabsolute pressure there is an immediate counter effect which opposessuch motion and prevents overtravel of the valve. The result is that theposition of orifice 34 and metering pin 33 relative to each other is somaintained as to meter theflow of air from the upper side of diaphragm-I 3, and

thereby cause valve I to seek a stable position."

Since this stable position of the valve'may vary considerably withchanges in the ventilating rate,

diiierential pressure, or in cabin leakage conditions, the linkagebetween valve I "and orifice plunger 32 isso arranged that the travelofthe valve is considerably greater than that of" the orifice, the-ratioof such movements in the particular installation pictured beingapproximately eight to one. In this wayneither' thepositionof' theorifice'3 i nor the critical cabin absolute presthe action of the spring(the. actual spring 30 or.

the bellows 3 considered as a spring occurs within a very narrow range;and hence there is substan: tially no change, during operation, in itseffective spring force. By change in the spring rate of the bellows unitor its spring, the limits of cabinpressure between the illustrativealtitudesof 8,000 feet and 30,000 feet may be made to follow curve bc"',or b-c", as shown in Figure 2. Similar results can be obtainedotherwisefor instance;

by changing the leverage ratio of the follow-up rocker arm 35,01 bychanging the relative size of the metering pin 33-and its orifice 34, orby two or more such changes combined} It may be pointed out'here thatthe value of'the critical limit can be altered, to start superchargingeither before or after reaching the 8,000 feet specified critical limitof low altitude operationi The critical limit can be lowered by movingupwardly the base as of the bellows 3.} Thereby in effect the springforce iesistingcollapse ofthe bellows 3 by the pressure on it of the airin casing 30 is increased. Also, by control of'the rate of upwardmovement of the base 38 the rate of. supercharging can-be controlled;These facts aremerely mentioned at this point, and theirisig- H it mustbe exaggerated in the drawings for purnificance and application will beexplained in" A piston 4 is exposed to cabin pressure on its lower sidethrough a vent 4!, and to atmospheric pressure on its upper side throughthe tube 42.

Cabin pressure, throughout isobaric operation, is

elevated above atmospheric pressure. At the critical differential ofcabin pressure over ex-' ternal pressure spring 43 is sufii'cientlycompressed by the upwardly moving piston 4 that the piston engages ashoulder 44 on the plunger 40. If, by reason of continued ascent and lowered external pressure, 'or'by'reason of increased cabin'pressure, thereis a tendency 'to exceed this differential, the plunger 40 is raisedupwardly'and separated from the stem it, to which it has heretofore beenheld by spring 3'! acting through lever 35. In practice theseparation isminute, only a few thousandths of an inch,-but

poses of clearer illustration; 'With the downward force'of spring 31on'the valve I- through lever' 35' and plunger Gil removed; the flow ofair'from the upper-side of the diaphragm l3 throughthe aperture 45 inthe plunger 40, by way of its ports 35 and the tube 42, reduces pressureabove the diaphragm l3 and causes the valve to open and relieve cabinpressure, as'explained previously.

Overtravel of the valve is prevented by the fact' that, as contactbetween the plunger t0 and the stem II] is broken by the action of thedifferential pressure 'controL'the valve assemblyfollows the plungerlll'upwardly by reason of the increased fluid pressuredifierentiala'cting on it, and tends to restrict the entry of air intothe bore 45' of the plunger. It is thus evident that an immediateresistance to further motion accompanics any increase in the lift of thevalve in response to action of the diiferential pressure control, andthat there will be no tendency for the valve'to hunt, or for cabinpressure to fluctuate. The absolute-pressure sensitive device 3 willextend toward its full upward travel as altitude is increased: andexternal pressure is lowered, so that the passage of air through theorifice 34 is eliminated by closure of the metering P1 1133, except fornegligible leakage.

,The stem It has been shown integral with the :through ahollow valvestem, and the cooper ating plunger 40 would then be solid, Such reversalis within the spiritof our invention.

For'brevity the piston 4 may be spoken of as the difierential-pressuresensitive device,'as the bellows'3 has been referred to as the absolutepressure sensitive device} While each of these is the'element' mostimmediately affected by such pressure conditions, itwill be realizedthat the: associated elements, together with and in theirrelationshipto. the elements 4 or 3, as a whole make up, respectively, thedifierentialpressure sensitive means and the absolute-pressure sensitivemeans.

Safety devices It is conceivable that negative pressure might fall. byreason of a sufiiciently rapid descent, or, if the source of lowpressure for operation of the diaphragm I3 or the piston 4 is the vacuumsystem of the airplane, it is conceivable that this might fail tofunction. In either case there would be a failure of negative pressurein such a way that there would be a tendency for the valve I to closeand remain closed, to an extent that atmospheric pressure might exceedcabin pressure. It is desirable to prevent the possibility of reversestresses, thus arising. A check valve I9 is normally seated to close ofian orifice that otherwise would afiord communication between the cabinpressure and the space 24 above the diaphragm I3.

Valve I9 is normally held seated by the differ ential pressure existingbetween the cabin and the chamber 24, which is normally at some pressurebelow cabin pressure. If the external pressure should exceed the cabinpressure this external pressure would communicate with the chamber 24,for instance through the tube 21, past metering pin 33, and through tube28, and

the valve I9 would then unseat and permit equalization of cabin pressurewith the external pressure, and would thereby assist in opening thevalve I by removing obstacles to its opening under the higher externalpressure acting upwardly upon it.

A normally open valve 21' may be included in the tube 21. If theabsolute-pressure sensitive device 3 should fail to function properly,it can be cut out by closing the valve 21. This leaves the limitingdifierential-pressure sensitive device 4 still fully operable, toprevent the cabin pressure exceeding the predetermined difierence overexternal pressure, and by suitable means the pressure supply can beaugmented or manually controlled, if necessary, to supply adequatepressure within the cabin.

Selective isobaric and dz'fierential pressure regulation The cabinpressure which will be maintained during operation under isobaricconditions may be altered, within practical limits, by altering theadjustment of the absolute-pressure sensitive device 3. This adjustmentmay be accomplished in various ways, for instance by altering thecompression of the spring 30, the compression in the bellows 3 itself,or the starting point or position of the base 38 and needle valve 33with relation to the orifice 34.

Practically speaking, such adjustment is readily accomplished byrotating the swiveled and internally threaded adjusting cap (or a cabledrum mounted thereupon) relative to the screw 50 which support the base38. If the cap 5 is rotated in a direction to raise the base 38, theelongation of the bellows which is required to produce the necessarymetering effect through the orifice 34 is decreased, and the criticallow pressure altitude at hich isobaric control commences (b in Figure 2)will be lowered. Contrariwise, if the cap 5 is rotated in a direction tolower the base 38, the elongation of the bellows 3 which is required toproduce the necessary metering effect through the orifice 35 isincreased, and isobaric regulation does not commence until a higheralti- 12 tude is reached; see, for example, line p-q in Figure 2.

In this way, and without more, the point at which isobaric regulationcommences may be adjusted at will and during flight. Adjustment of thestarting point, however, will not affect the nature of the graph, Figure2, nor affect the essential nature of operation of the absolutepressuresensitive device 3 nor of the differentialpressure sensitive device t.No such adjustment of the starting point of isobaric regulation, as fromb to p, can affect the initiation of difierential pressure operationwhen the limiting differential is reached. In other words, no adjustmentof the pressure which is maintained during isobaric regulation can causethe difierential-pressure sensitive device to fail to operate when theselected difierential of pressure is attained, along the line n-c-d.

The cabin difierential pressure which will be maintained duringoperation under maximum limit is to a small extent adjustable (see line4, Figure 2) by means of a needle valve I8, which controls communicationbetween the upper and lower sides of the piston 3. In the drawing suchpiston has been shown as the preferred arrangement, but the differentialpressure controlability of the unit will function equally well if adiaphragm similar to I3 be used. It is clear that if the air leakagearound piston 4 is negligible, the difierential pressure across thepiston I2 will be substantially equal to the difierence between cabinpressure and atmospheric pressure. Then if a leakage be induced eitherby increasing the clearance between the piston and the cylinder, or byopening needle valve I8, there will be a small pressure loss from thechamber below the piston to the tubing 42, or a small increase inpressure above the piston, or both, either or both of which changes willin turn reduce the differential pressure acting upon the piston.Likewise it is evident that a small increase in leakage through thevalve I8 is equivalent to an increase in the elastic properties of thespring 43. By adjustment of the valve I8 the value of the differentialpressure may be altered to increase or to decrease it.

It i possible to obtain any desirable range of adjustment of both theabsolute and differentialpressure control elements by the propervariation of the effective elastic properties of the springs 30 and 43,according to expedients which are universally employed for springadjustments.

Compensating needle valves Adjustment of needle valve I6 permits theproper coordination of the passage of air from the cabin to the upperside of the diaphragm I3 with the restrictions arising from eachindividual installation of tubes 21 and 42. Also it serves as convenientadjustment of the leakage to chamber 24 and thence out through theabsolute pressure sensitive control, which leakage efiectively controlsthe stability of operation of the control valve I when under isobaricregulation.

Needle valve I5 has been provided for the purpose of compensating forvarying clearances around the lip of valve I and permits the propercoordination of the leakage into chamber IT with the leakage out throughholes I4. In other forms of the device it might serve the purpose ofvarying the damping effect of the air entrapped above valve I in chamber[1.

Rate of pressure change control As has already been pointed out, thecabin pressure, between the lower limit fixed by the atmosphericpressure: curve a b "c'd' and theuppe'rliinit fixed -by thedifferential'pressure curve nc-d, may be varied by adjustment: of themetering-valve 33"with respect to -its orifice 34, or vice versa. It hasalready been pointed out that such an adjustment may be accomplished byadjustment of the position, up or down, of the base 3'8. Such adjustmentas heretofore-explained was for the purposeof determining andadjusting'the initial point (b to p) and absolute value ofisobaricregulations. However, such adjustment can also be used for the furtheror somewhat different purpose of imparting a time element and ofaccomplishing increase or decrease of pressure ata'ny point,fromsea-level to the ceiling of the pressure supply system, withinthelimit fixed by the-differential pressure control device,independently of orat'a' rate difierent'from that normany-required byascentor descent.

To illustrate by reference to Figure 2, a pilot taking off from sealevel at pressure amay intend to ascend as rapidly as possible toanaltitude which is above that represented at 0. Instead of attempting tofollow the substantially unsupercharged curve a-b and thence by way of bto c, the pilot may prefer to decrease his cabin pressure at a ratewhich-will bring him to the value c at the time, having in mind hisrateof climb, that he will reach the altitude represented at 0. Or, he maywishto lower his cabinpressure at a rate which will bring him back tothe line b-c at the points; and thence forward he may followtheline-e--c-d, or he may wishto continue at a substantially constantrate of' decrease of cabin pressure from etc I, and soon until hereaches the differential pressure limit cd. Again, after he has climbedfor some distance, hemay, at an altitude corresponding to g, wish todecrease his cabin pressure at a-rate which will bring him on the curvebc at the point h, and thereafter he may follow the curve hcd; Indescending he may be at an altitude corresponding to the point :i, andin anticipation of a later descent, but without actually descending, hemay increase his cabin pressure, as indicated fromy' to k, and thenfurther decrease it from k to m, representing the pressure'at hislanding'field, and thus, while several thousand feet above his landingfield, but still well within the permissible differential; he may attainwithin the cabin a pressure corresponding to the pressure at the landingfield; By such means hemaylessen therate of cabin pressure rise or fall,so that passengers and crew may become more gradually'accustomed to thealtered pressure,

By the use of the basic cabin pressure control already described; theseends can be attained simply by governing the rate of rotation of thescrew cap'5 or equivalent means, and by governingv thereby therate'ofrising or lowering of the base'38'. A suitable means foraccomplishingthis operation is illustrated diagrammatically in Figure 5,- wherein 6'represents a reversible variable speed motor operatively connected byany suitable drive means to the cap for moving the base 38- at acontrolled rate and in either sense.

The means for rotating the motor and for controlling its-speed may beany that are desired, and that shown herein is to be understood asmerely representative of any one of several means that could beemployed. For instance, til represents a rheostat to control the speedof the motor, and 51' a reversing switch to control its sense ofrotation. In addition it maybe provided with a meanswhich'is-automatically capable ofst'oppin'g 14 the motor. after a given?time intervalsor after a given'numberiof rotations- Thus, for example,53' represents a settable ccntactarm engageable with any one of a numberof contacts Sta, 5%, 640, etc. We may assume that it is set in contactwith the point Me. The contact arm 62, driven by or synchronized withthe motor 6, rotates past a series of contacts 65a,

65b, 55c, etc., corresponding to and connected each with its respectivecontact 54a, 641), etc. Current from a source represented at 66 maypass, when the rotating contact arm 62 engages the contact point 55c, byway of the settable' arm 63 and the rotatable arm-e2 to an electromagnet61, which upon being energized opens a switch 68' in the circuit of themotor 6, and stops the operationofthe motor. Alternatively the arm 53may be motor-driven, inwhich case the other arm E2 will-bethe settablearm.

By such an arrangement it is possible to regulate the speed of themotor, its sense of rotation, and the time period during which it is tooperate. By control of these factors, acting to rotate the screw cap 5in one or the other sense for a selected period of time and at aselected rate of rotation, it is possible to achieve change of pressurewithinthe cabin at any rate desired, whether for increase or decrease asdesired, and throughout any time period desired.

Nevertheless, with any" possible adjustment of the screw cap 5 and ofthe absolute-pressure sensitive device 3 whichis thereby entailed,the'differential-pressuresensitive device 4 is always capableoffunctionin and does function to prevent, under any conditions, theexceeding of the selected differential of pressure represented at cc inFigureZ.

Balancing of pressure supply meanswi'th the" pressure control device Thearrangement of Figure 3 shows the pressure control device as completelyindependent of the pressure'supply device, althoughthe two will bebalanced in their design, so that such necessary pressure will besupplied at all altitudes as can be properly controlled by thepressure-control device. This particular arrangement contemplates aconstant rate of flow, but a variation in the speed of the blower tomaintain the flow constant under difierent pressure conditions. Brief lythe arrangement illustrated in Figure 3 includes aservo piston 93ccontrolled by a pilot valve 93d and controlling the hydraulic changespeed gearing 92. The pilot valve 9301 is under the control of apressure-sensitive device represented as the diaphragm 93c within thecasing 93a, subjected on the one side to minus pressure through the tube95 and on the other side to plus pressure through the tube 84, whichpressure difference is a function of flow into or through the cabin. Thearrangement is such that, regardless ofthe absolute pressurebeing'maintained in the cabin by its automatic pressure control, andregardless of the pressure rise that the blower must maintain to producethat pressure, the blower will be speeded up, as required, to maintain asubstantially constant flow of air intothe cabin.

In Figure 4 the arrangement is the same as that in Figure dexcept thatthe lower pressure side of the pressure regulator era has connected toit a tube 93?) leading from within the cabin. However, this tube 931) isnot normally in communication with the plus pressure inth e cabin. Theplunger 40- is normally interposed as a valve between the cabin pressureand the interior of the tube 93b. The plunger 4c, however, has anaperture 40' which may afford communication between the interior of thetube 931) and the cabin. Such communication occurs when the valve 1 byreason of dropping cabin pressure, approaches closed position, therebyapplying the cabin pressure as a plus pressure to the low pressure sideof the diaphragm 93c, tending to equalize the pressures on the two sidesof this diaphragm, and destroying the low pressure effect on thenormally low pressure side, and thereby reacting to adjust the blowercontrol to speed up the blower. Thus cabin pressure is prevented fromdropping and is maintained substantially constant by the speed-up of theblower, and the air supply is balanced against the outflow from thecabin. Any undue increase of cabin pressure can be avoided by normaloperation of the pressure control devices, or the interconnection can beso arranged as to decrease the blowers speed correspondingly.

We claim as our invention:

1. Mechanism for controlling the pressure of air within an aircraftcabin to which air under pressure is supplied, comprising pressurecontrolling means responsive to cabin pressure and operableautomatically to regulate the cabin pressure, and motor drive meansoperatively connected to said pressure controlling means and operable toadjust the same at a predetermined rate, to alter the cabin pressurefrom that normally effected by said automatic regulating means and at arate corresponding to the rate of adjustment of said pressurecontrolling means effected by said motor drive means.

2. Mechanism for regulating aircraft cabin pressure, comprising a valvemovable to control flow of air through the cabin, valve actuating meansnormally operable to regulate said valve for maintaining the aircraftcabin pressure at a substantially constant value, motor drive means, andmechanical thrust-producing means interconnecting said motor drive meansand said valve actuating means and operable to drive the same at apredetermined rate by operation of said motor drive means to alter theposition of said valve, and consequently the cabin pressure, at acorresponding rate.

3. Mechanism for regulating aircraft cabin pressure comprisingregulating means movable to control flow of air through the cabin,actuating means normally operable to control said regulating means formaintaining the aircraft pressure at a substantially constant value,drive means operatively connected to said actuating means and operableto adjust the same for effecting operation of said regulating means toalter the cabin pressure at a rate corresponding to the rate ofadjustment of said regulating means, and means driven by said drivemeans and operatively connected to said drive means, and operable toterminate operation of said drive means upon completion of apredetermined movement thereof corresponding to the total alteration incabin pressure desired.

4. Mechanism for regulating aircraft cabin pressure, comprising a valvemovable to control flow of air through the cabin, valve actuating meansnormally operable to regulate said valve for maintaining the aircraftcabin pressure at a substantially constant value, motor drive meansoperatively connected to said valve actuating means and operable todrive the same at a predetermined rate to alter the position of said 16valve, and consequently the cabin pressure, at a corresponding rate, andcontrol means driven by and operatively connected to said motor drivemeans, and operable to terminate operation of said motor drive meansupon completion of a predetermined movement thereof corresponding to thetotal alteration in cabin pressure desired.

5. Mechanism for regulating aircraft cabin.

pressure, comprising a valve movable to control outflow from the cabin,a pressure responsive means subject to cabin pressure and including anevacuated bellows having a support at one end, means connected to themovable end of said bellows and operatively connected to control saidvalve in accordance with axial expansion or contraction of the bellowsto eifect movement of said valve for maintaining cabin pressure at onepredetermined, substantially constant value, and adjusting meansoperable to set said pressure responsive means for maintaining cabinpressure at different substantially constant values, and motor drivemeans operatively connected to said adjusting means and operable toshift the same at a predetermined rate to adjust said pressureresponsive means, and consequently said cabin pressure value, to changeat a corresponding rate the constant cabin pressure setting of saidpressure responsive means, and in turn to alter the cabin pressure.

6. Mechanism for regulating aircraft cabin pressure defined in claim 5,and spring means tending to expand said bellows, the adjusting meansbeing operable to adjust said spring means for altering the degree ofbellows-expanding force exerted thereby on said bellows, to set thepressure responsive means.

'7. Mechanism for regulating aircraft cabin pressure, comprising a valvemovable to control outflow from the cabin, a pressure responsive meanssubject to cabin pressure and including an evacuated bellows having asupport at one end, and means connected to the movable end of saidbellows and operatively conected to control said valve in accordancewith axial expansion or contraction of the bellows to effect movement ofsaid valve for maintaining cabin pressure at one predetermined,substantially constant value, said bellows support being movable to setsaid pressure responsive means for maintaining cabin pressure atdifferent substantially constant values, and motor drive meansoperatively connected to said bellows support and operable to shift thesame axially at a predetermined rate to adjust said pressure responsivemeans, and consequently said cabin pressure value, to change at acorresponding rate the constant cabin pressure setting of said pressureresponsive means, and in turn to alter the cabin pressure.

8. Mechanism for controlling the pressure of air within an aircraftcabin to which air under pressure is supplied to supercharge it,comprising control means responsive to cabin pressure including anadjustable member for regulating the air pressure in the cabin, anelectric motor for moving said adjustable member, and means forregulating the speed of said motor for controlling the rate at which achange in setting takes place.

9. Mechanism for regulatin aircraft cabin pressure, comprising anoutflow valve, fluid-operated servo means operatively connected to movethe valve, means movable to govern flow of fluid through said servomeans, motor means operable to move said fluid flow governing means, andselective deenergizing means settable to effect deenergization of saidmotor means after completion 17 of predetermined movement thereofselected by setting of .said .deenergizing means, thereby to establishthe desired displacement of said moving means operative to alter theposition of said valve, and consequently the cabin pressure.

.10. .Mechanism for regulating aircraft cabin pressure, comprising anoutflow valve, fluid-operated servo means operatively connected to movethe valve,.means movable togovern flow of fluid throughsaid servo means,moving means operable to move said fluid flow governing means, meanssettable to establish the extent of movementof said moving means,andmeans operable to select the .rate of movement of said moving .means,thereby to establish the time period during which said moving means isoperative to alter the position of said valve, andconsequently the cabinpressure.

'11. Mechanism for regulating aircraft cabin pressure, comprising anoutflow valve, servo means operatively connected to the valve, controlmeans operable to control said servo means by effecting thereon avalve-opening force which varies in accordance with the difference ofcabin pressure over external pressure, whereby to prevent the cabinpressure from exceeding a selected differential over externalpressure,and pressure changing control means also operable to control said servomeans, including operating means operable at willto eifect movement ofsaid valve by the servo means and therebyto effect change of cabinpressure regardless of change of altitude or rateof change of altitudeof the aircraft, means settable'to preselect the extent of operation ofsaid operating means within the limiting differential of cabin pressureover atmosphericpressure establishedby said control means, anddeenergizing means controlled by said settable means and operativelyconnected to said operating'means to deenergize the same at completionof the extent'of operation for which said settable means are set andattainment of the corresponding-degree of changein cabin pressure.

12. Mechanism .for regulatin aircraft cabin pressure, comprising anoutflow valve, servo means operatively connected to the valve, controlmeans operable to control said servo means by efiectin'g thereon avalve-opening force which varies in accordance with the difference ofcabin pressure over external pressure, whereby to prevent thecabinpressure from exceeding a selected differential over externalpressure, and pressure changing control means also operable to controlsaid servo means, including variable speed electric motor meansoperableat will to drivesaid valve at a substantially .constant speed by theservo means and thereby to efiect change-of cabin pressure at asubstantiallyconstant rate regardless of change of altitude or rate ofchange ofaltitude of the aircraft, .and means settable topreselecttherate. of operation ofsaid electric motor means to establishthe desiredconstant rate o'fchange incabinpressure.

1.3. Mechanism for regulating aircraft cabin pressure defined. in claim12, and-means settable to .preselectthe extent of operation of theelectric motor means toestablishthe degreeof change in cabin pressureproduced, and hence the time period within which-such changein cabinpressure occurs.

14. Mechanism -'for regulating the pressure within an aircraft cabin,comprising regulating means movable to regulate the pressure in thecabinpcontrol means operable to control said regulating means tomaintain a desired pressure in the cabin,-including pressure sensitivemeans, spring means exerting a force on said pressure sensitive means,and amember movable to change the setting of said spring means forvarying the force exerted thereby ,on saidpressure sensitive means,power means operable to efiect movement of said-member, andadjustablemeans settable to establish the rate at which said power means movessaid member to vary the force of said spring means on said pressuresensitive means, for controllingthe rate at which cabin pressureisaltered by said regulating means.

15. In cabin pressure control mechanism, a pressure sensitive controlelement operable to controlregulation of the cabin pressure, springmeans exerting a force on said pressure sensitive element, adjustingmeans movable to alter the force exerted by said spring means onsaidpressure sensitive controlelement, motor meansoperable to drive saidadjusting means for altering progressively the force exerted by saidspring means, and settable means capable of being preset to controltherate atwhich said motormeans drives said adjusting means.

16. Mechanism for controlling the pressure-of air in an aircraft cabin,comprising pressure regulating means operable to control flow -,of ,airthrough the cabin, means sensitive to fluctuations in cabinpressure forcontrolling the operation of said. pressure regulatin means tending tomaintain cabin pressure at aselectedvalue and includingabsolute pressureresponsive means .responsive to a pressure related to cabin pressure,spring means exerting a force onsaid absolute pressure responsive means,motormeansoperable to adjust said spring means for varying the forceexerted thereby on said absolute pressure responsive means so as tochange the selected valueof pressure maintained by said sensitive meansand settable control means operable to control operation of said motormeans and settable to effect predetermined operation thereof.

1'7. Mechanism for controllingthe pressure-of air in an aircraft cabin,comprisingpressure regulating means operable to control flow of :airthrough the cabin, servomotor means including a chamberand a pressureresponsive element in said chamber and connected to said pressureregulating means for operating the same in response to changes indifferential pressure on opposite sides of said element,,a pilot valveproviding. for the controlled escape of air fromsaid chamber at one sideof said element to aregion oflower pressure, absolute pressureresponsive means in communication with the cabin and operable .tocontrolsaid pilot valve tomaintain a selected pressure in said chamber,motor means operable to adjust said absolute pressure responsive meansto control said pilot-valve for establishing a dif-- ferent pressureinsaid chamber, and settable control means operable to controloperationof said motor means and settableto eifect predeterminedoperation thereof.

18. Mechanism for controllingthe pressure of air within an aircraftcabin, comprisingpressure regulating means operableto control flowof'ai'r through the cabin, servomotor means including a chamber and apressure responsive element'in said chamber and connected tosaidpressureregulating meansfor. operating the same in response tochanges ingdiiferential pressure on opposite sides ofsaid, element, thepressure actingagainst one side of said element being cabin pressure,

means having a restricted aperture for limited bleeding of cabin airinto said chamber at the other side of said element, a pilot valve forcontrollin the escape of air from said chamber at such other side ofsaid element to a region of lower pressure, absolute pressure responsivemeans responsive to a pressure'related to cabin pressure and operable tocontrol said pilot valve, means operable to adjust said absolutepressure responsive means to control said pilot valve for maintaining adifierent pressure in said chamber and thereby change cabin pressure,motor means for automatically operating said adjusting means, and meanscontrolling said motor means to efiect operation thereof at apredetermined rate in changing the pressure within said chamber at, suchother side of said element.

19. Mechanism for controlling the pressure of air within an aircraftcabin, comprising presure regulating means operable to control flow ofair through the cabin, servomotor means including a chamber and apressure responsive element in said chamber and connected to saidpressure regulating means for operating the same in response to changesin difierential pressure on opposite sides of said element, the pressureacting against one side of said element being cabin pressure, meanshaving a restricted aperture for limited bleeding of cabin air into saidchamber at the other side of said element, a pilot valve for controllingthe escape of air from said chamber at such other side of said elementto a region of lower pressure, absolute pressure responsivemeans-responsive to a pressure related to cabin pressure and operable tocontrol said pilot valve, means operable to adjust said absolutepressure responsive means to control said pilot valve for maintaining adifferent pressure in said chamber and thereby change cabin pressure,power means operable to actuate said adjusting means, selectivelyvariable means operable to control the operation of said power means atvarious selected rates, means operable to select a difierent value ofcabin pressure desired, means driven by said power means in synchronismwith said adjusting means, and means cooperatively controlled by saidcabin pressure selecting means and by said driven means and operable toterminate the operation of said power means when the cabin pressurereaches such diiferent selected value.

20. Mechanism for regulating the pressure within an aircraft cabin,comprising pressure regulating means operable to control flow of airthrough the cabin, absolute pressure responsive means responsive to apressure related to cabin pressure, means controlled by said absolutepressure responsive means and operable to control said pressureregulating means for maintaining the cabin pressure at a selected value,means operable to adjust said absolute pressure responsive means, anelectric motor operatively connected to drive said adjusting means,switching means driven by said electric motor in synchronism with saidadjusting means, a plurality of electric circuits selectively closableby said switching means and each corresponding to a different selectedvalue of cabin pressure, manual switching means operable to select theone of said electric circuits corresponding to the difierent cabinpressure desired, and motor control means operable by energization ofthe one of said electric circuits selected by said manual switchingmeans to interrupt operation of said electric motor for terminatingmovement of said adjusting means when the cabin pressure has reachedsuch selected 20 difierent desired value corresponding to the one ofsaid circuits selected by said manual switching means, upon closingthereof by said driven switching means.

21. Mechanism for regulating the pressure within an aircraft cabin,comprising a valve operable to control the flow of air through thecabin, absolute pressure responsive means responsive to a pressurerelated to cabin pressure, means controlled by said absolute pressureresponsive means and operable to move said valve to maintain the cabinpressure at a selected value, means operable to adjust said absolutepressure responsive means, a reversible electric motor operativelyconnected to drive said adjusting means, means operable to regulate therate of operation of said adjusting means by said reversible motor, andmeans operable to interrupt operation of said electric motor when thecabin pressure has reached a predetermined value.

22. Mechanism for controlling the pressure of air in an aircraft cabinprovided with airflow means for circulating air under pressure throughthe cabin, comprising valve means, means for operating said valve meansso as to maintain a selected pressure in the cabin, absolute pressureresponsive means for determining said selected pressure, motor meansoperable to actuate said absolute pressure responsive means to select adifierent pressure, selective control means operable to efiect operationof said motor means at a predetermined speed to actuate said absolutepressure responsive means at a speed corresponding to that for whichsaid selective control means are set, at which to maintain cabinpressure.

23. Mechanism for controlling the pressure of air in an aircraft cabindefined in claim 22, and means operable to control said motor means toestablish the rate at which the absolute pressure responsive means isactuated by the control means in conforming to a new setting thereof.

24. Mechanism for regulating pressure within an aircraft cabin,comprising valve means closable to restrict outflow and thereby to raisecabin pressure above ambient atmospheric pressure,

control means operable to exert a closing force on said valve means,power means operable to adjust said control means to increase theclosing force on said valve means effected by said control means,energizing means operable to energize said power means and presettablein varying degrees to establish the extent of variation in forceeffected by said control means on said valve means, and deenergizingmeans operable to deenergize said power means when the force effected bysaid control means on said valve means has been varied to the degree forwhich said energizing means was preset.

25. Mechanism for regulating pressure within an aircraft cabin,comprising valve means closable to restrict outflow and thereby to raisecabin pressure above ambient atmospheric pressure, control meansoperable to exert a closing force on said valve means, power meansoperable to adjust said control means to increase the closing force onsaid valve means effected by said con trol means, energizing meansoperable to energize said power means and presettable in varying de- Icontrol means on said valve means has been,

varied to the degree for which said energizing means was preset, andmeans operable to control 21 said power means and presettable toestablish the speed of movement thereof and consequently the rate ofchange in force exerted by said control means on said valve means.

JAMES B. COOPER. ALFRED B. JEPSON.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Price July 16, 1940 Number Number Number

